1. Field of Invention
The present general inventive concept relates to feeders and conveyors, and more particularly, to a linear motion conveyor useful in conveying bulk materials.
2. Description of the Related Art
Various types of conveyors and feeders (hereinafter, collectively, “conveyors”) are known for use in conveying bulk materials. In a typical conveyor, force may be applied to, for example, bulk materials in one or more directions in order to move materials from one location to another. For example, in a linear conveyor, force may be applied to bulk materials in order to move the materials along a linear direction. Linear conveyors are often employed, for example, to move bulk materials adjacent or through other machinery or workers which may be employed in a fabrication or packaging process.
Two common types of linear conveyors are belt conveyors and pan conveyors. In a belt conveyor, two or more pulleys are provided with an endless loop of flexible material surrounding them. The endless loop forms a carrying surface, and the pulleys are rotated to move a top portion of the carrying surface from one pulley toward the other. A pan conveyor typically employs a solid conveying surface, known as a “pan,” which is turned up on the sides to form a trough shape. The pan is typically set at a slight angle to the horizontal and is subjected to motion, such as vibration or oscillating motion, in order to move the materials along the pan, often with the assistance of gravitational forces acting on the materials.
In some instances, pan conveyors may be preferred over belt conveyors or other types of conveyors where sanitation is a concern, such as in the food or pharmaceutical industries, due to the relative ease in cleaning the pan of a pan conveyor as compared to the conveying surfaces of other types of conveyors. Furthermore, a discharge end of a pan conveyor may be formed to define a beveled, or “biased,” shape, such that the biased pan conveyor may discharge bulk materials in a relatively even layer along a subsequent linear conveyor. Thus, pan conveyors are often preferred where two or more conveyors are required to merge at angles, and where it is desired to spread product evenly over the width of the subsequent conveyor.
Notwithstanding the above, the use of pan conveyors to convey certain types of bulk materials may pose significant limitations. For example, a pan conveyor which employs vibration of the pan to convey material may subject the material to significant impact forces due to the vibratory action of the conveyor, and can therefore result in damage to the conveyed material. Thus, in circumstances in which breakage of product is a concern, such as for example when fragile food products, such as potato chips, flake cereal, etc., are being conveyed, vibratory pan conveyors are typically less desirable. A pan conveyor which employs linear oscillation of the pan along the direction of travel to convey material is dependent upon an alternating sliding and frictional relationship between the conveying surface of the pan and the material to be conveyed, such that a forward action of the pan urges material in a forward direction along the conveyor, while a backward action of the pan allows the pan to slide beneath the forward-moving material with minimal interruption of the forward movement of the conveyed material. This type of “adhere-slide” relationship can be difficult to establish, thus requiring significant startup time for this type of conveyor. Furthermore, the “adhere-slide” relationship of the pan and materials to be conveyed is often dependent upon the specific weight and frictional characteristics of the materials to be conveyed, thus requiring fine-tuning of the pan conveyor in order to effectively convey the bulk materials.
The use of linear actuators driven by electric motors with programmable stroke lengths has been previously explored as a solution for some of the aforementioned limitations. Linear actuators consist of two elements which can be made to move relative to each other along a single axis. When one element is mounted to a fixed surface, the other element can be set into motion and a thrust force is produced in line with the moving element. If motion is induced dictated by a cyclic profile featuring a high-thrust reverse motion followed by a low-thrust forward motion, the linear actuator can be used as a horizontal motion drive. However, linear actuator designs present unique challenges of their own. Mechanical mounting arrangements can introduce unwanted vertical force vectors and limit stroke length. Thrust rod designs based on either rotary-driven screws or annular linear motors typically require close-tolerance machining and robust guiding to avoid destructive axial loading. Flat linear motor designs require even more exacting machining, owing to the precise air gap that must be maintained between the motor coils and the permanent magnets along the axis of travel.
In light of the above, a linear conveyor which addresses some or all of the afore-mentioned limitations is desirable.